In U.S. Pat. No. 4,398,994, assigned to the assignee hereof and the disclosure of which is incorporated herein by reference, there is described a continuous method of forming decorative patterns of aluminized plastic film and the use of such patterned film in packaging.
As described therein, a web of aluminized polymer film is printed with a pattern of etchant-resistant material, corresponding to the pattern desired to be retained on the aluminized surface. Aqueous sodium hydroxide solution is applied to the patterned film to etch away the exposed aluminum while the aluminum covered by etchant-resistant material is untouched.
In U.S. Pat. No. 4,552,614, assigned to the assignee hereof and the disclosure of which is incorporated herein by reference, there is described an improved procedure to effect such selective demetallization by employing spray application of the aqueous etchant to the patterned aluminized surface.
More recently, in U.S. Pat. No. 4,869,778, it has been proposed to form a micropattern on the aluminized surface by first contacting the patterned aluminized polymeric film with a warm, essentially saturated caustic solution followed by contact with an acidic solution and washing.
The procedures described in the aforementioned prior art are very effective in achieving selective demetallization of relatively thin aluminum layers (generally less than about 1000 .ANG. in thickness) supported on a polymeric web to completely remove aluminum from selected areas of the surface of the polymeric web for a variety of purposes, such as in decorative packaging and in microwave susceptor applications. The procedures, however, are less effective with relatively thick aluminum layers supported on a polymeric material web or unsupported because of rapid depletion of the etchant in contact with the web by the etched material.